Diode disconnect circuit, for electronic musical instruments, isolating variable load means from tone generator means



. R. BRAND July 26, 1966 J DIODE DISCONNECT CIRCUIT, FOR ELECTRONIC MUSICAL ISOLATING VARIABLE LOAD INSTRUMENTS,

MEANS FROM TONE GENERATOR MEANS Filed June 21, 1963 MASTER OSCILLATOR 20A\ QIOA V42 M51. 5 aurPl/f L 0/: D

an? 00/7 MEANS WE/ABI. E 01/7/ 0 T L 040 C/EGU/T INVENTOQ JOHN R. .BQQND BY W 7? ATTORN E Y United States Patent DIODE DISCONNECT CIRCUIT, FOR ELECTRONIC MUSICAL INSTRUMENTS, ISOLATING VARI- ABLE LOAD MEANS FROM TONE GENERATOR MEANS John R. Brand, Northridge, Calif., assignor, by mesne assignments, to Warwick Electronics Inc., Chicago, 111., a corporation of Delaware Filed June 21, 1963, Ser. No. 289,594 Claims. (C1. 84-1.01)

This invention relates in general to tone generators, especially as employed in electronic musical instruments, but it relates more specifically to a disconnect system to control a wave form output of a tone generator, and to protect the generator from outside load influences.

This invention is especially suited for electronic musical instruments, such as electronic organs, and therefore the description of the preferred embodiment of the invention herein will be directed to a circuit suitable for such an environment.

In a typical electronic organ environment, master oscillators are used to produce the basic frequency from which various voices and eifects are created.

Such master oscillators or generators are designed to produce a useful frequency 'and magnitude. The generators may be designed to work into any given load and produce a consistently uniform effect. In the typical organ the output load of such a generator may vary widely and consequently the frequency and magnitude of the oscillation may be distorted, and hence the final output sound from the audio system will not be as clear and perfect as desired.

Accordingly, it is .an object of the present invention to provide a tone generator system for electronic musical instruments which is relatively unaffected by variations of output load.

It is a further object of the invention to provide a tone generator system producing a resultant substantially rectangular type of output frequency wave form from an originally created wave form of non-rectangular shape.

It is a further object of the invention to provide a diode disconnect system to both isolate a tone generator from output loads, and to limit the magnitude of output oscillation in order to provide a uniform rectangular wave form output.

In accordance with these and other objects which will become apparent hereinafter, a preferred form of the present invention is disclosed in the accompanying drawings wherein:

FIGURE 1 is a circuit diagram of the tuned oscillator system employing a diode disconnect principle according to this invention;

FIGURE 2 is a wave form chart;

FIGURE 3 is a circuit diagram of a bistable tone generator which produces a substantially rectangular wave form, and is controlled by a diode disconnect according to this invention; and

. FIGURE 4 is a wave form chart.

In FIGURE 1 of the drawing there is illustrated a transistor having -a collector output 11 and an emitter 12 connected to ground 13. The balance of the circuit illustrated is not specifically described, being a common resonant frequency master oscillator of a type well known in the art.

This type of oscillator operates to produce an output wave form 'at 11 such as illustrated in the chart of FIG- URE 2. The low value part of this wave form is produced by the action of transistor 10 being biased to conduct in saturation to ground 13. When so conducting, varying loads placed upon the collector at 11 have little or no efiect upon the oscillator.

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In the cycle of operation, the transistor 10, after a period of time, ceases conducting almost instantaneously. In the the wave form diagram of FIGURE 2, the result of the conduction period is shown as that portion of the curve indicated by the reference character 20 lying substantially, although not absolutely, at the zero voltage abscissa line of the chart. Whenever the transistor 10 ceases conduction, the voltage which appears across the resistance 21 at the output 11, begins to build up from the low voltage to the maximum voltage in a substantially instantaneous period of time, as shown by the rising curve portion 21 of the wave form period. Although the transistor is supplied from a 15 volt power source, the fly wheel etfect of the tuned system will carry the wave to 20 or more volts. However, with time as the voltage increases, the curve 210 becomes greater until an apex region 22 is reached at the maximum voltage.

Shortly after reaching the apex voltage 22, the tuned system causes transistor 10 to begin conducting again, and almost immediately upon commencement of conduction, the conduction goes completely to saturation, and the curve is substantially vertical in the area 23. Thus, there is completed a cycle of output from the tuned oscillator as shown in FIGURE 1. The oscillator, as thus far described, is a sensitive system whose output frequency, amplitude, and wave form may beseriously affected if loaded indiscriminately. Also since the master oscillator is usually used to drive a bistable or similar type frequency divider which produces a rectangular output wave form, it is desirable to likewise produce from the master oscillator a substantially rectangular wave form, such as illustrated in FIGURE 2 to the right of the full Wave form, without variation because of such loading. Here it will be seen that the wave form is created by an upright section 210A, at constant maximum voltage line 222A, and a return, substantially vertical side 23A. This rectangular type wave is useful as a source for electronic musical instruments.

According to this invention, the full wave form shown to theleft side of the chart is converted into the useful wave form appearing at point 35 shown on the right side of the chart in FIGURE 1, and the oscillator is protected from outside loads in order to maintain the frequency constant and of the desired fixed maximum amplitude.

To accomplish this result, an output isolator device is provided. In the drawing of FIGURE 1, such device is illustrated as diode 30. This isolator device 30 is characterized by the ability to conduct substantial current loads in one direction, and to conduct substantially no current in the opposite direction. A diode is an ideal fulfillment of this defined characteristic.

' This invention employs devices which are controlled by balance of voltagea device which conducts current more easily in one direction than the other. This is the definition of a diode given in Modern Dictionary of Electronics, published by Howard Sams & Co., First Edition, page 77. Hence, for simplicity, the balance of this description will refer only to diodes for the purpose of explanation.

- In the FIGURE 1, a resistor 31 is connected to ground and to the anode side 35 of diode 30. A source of voltage indicated by the reference character 32 operates through a resistor 33 and is also connected to the anode of diode 30. This voltage divider system provides a potential of about 9 volts to the diode 30.

P Therefore, when the transistor 10 is conducting to saturation into the ground 13, the 9 volt system will conduct current through the diode and transistor to ground, and the voltage at the anode side 35 of the diode 30 will he near zero. Note that the bottom portion 20A of the rectangular wave in the Wave chart is higher above the zero abscissa than the bottom portion of the master oscillator wave form due to the voltage drop across the diode 30, and transistor Whenever the transistor 10 ceases to conduct, and the voltage on the collector 11 rises, the voltage on the anode side 35 of the diode 30 will follow until 9 volts is reached, whereafter the voltage will cease to follow the generator and will hold steadily at the specified voltage of about 9 volts as suggested by the dotted line 22B bridging between the sides 21 and 23 in the full wave form of the chart.

After the generated wave passes point 22 and returns along the side 23 to the 9 volt level, the voltage on the anode side of the diode 30 drops sharply, along with the collapse of the generated wave, down to substantially zero once again. Thus, the output wave on the anode side of diode 30 is substantially that shown in the rectangular form to the right in the wave form chart FIGURE 2, and will be seen to be the lower portion of the full wave form to the left. The sides 210A and 23A, therefore, are not precisely vertical as would be ideal, but are sufficiently close for the purposes intended.

As thus described, the full wave form of the generator is converted into a useful rectangular wave form, but in addition the sensitive generator is not disturbed by outside loads, (because when the diode 30 is conducting, transistor 10 is under saturation current and therefore there is no possibility of disturbing the generator. Conversely, when the diode 30 is not conducting, then it does not matter what kind of loading is placed on the outside circuit, because diode 30 isolates the generator from such outside influences.

The FIGURE 3 of the drawing illustrates a bistable type of tone generator. The purpose of showing the FIG- URE 3 is to illustrate the fact that the present invention is operable wit-h any type of tone generator, the only limitation being that the output of the tone generator must be operable with an output means which alternately shunts the output to a low potential, or even to zero potential at ground. In both instances, that is in FIGURE 1 and FIG- URE 3, this effect is obtained by the use of a transistor.

In the FIGURE 3, the diode 30 is shown to be biased by a source 32A operating through a resistance 33A. In this instance, the voltage is supplied across the resistance at the desired level of operation rather than to use a voltage divider. The operation and effect is identical to that described in connection with the voltage divider of FIG- URE 1.

In the bistable generator of FIGURE 3, a substantially rectangular wave, as shown in the Wave form chart of FIGURE 4, is produced from the collector 11A at 2. voltage peak above that desired for the output. During the period when the transistor 100 is cut off, the diode 30 will be reverse biased and no current will flow from the source 32A through the diode, and consequently the voltage appearing at point 35A during this interval will be the full 9 volt potential of source 32A. During the period when the transistor is conducting heavily the diode 30 will likewise be conducting and the potential at point 35A will be near zero but slightly higher than the corresponding potential at 11A due to the voltage drop across the diode 30. It will then be seen that the peak to peak output voltage of the multivibrator and diode disconnect system in FIGURE 3 corresponds very closely to that of the master oscillator and diode disconnect system of FIG- URE 2. Thus for all frequencies required by the musical instrument whether they be generated by the master oscillat-or or the bistable dividers, the output wave form will be essentially rectangular and of approximately the same amplitude.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention which is therefore not to be limited to the details disclosed herein but is to be afforded the full scope of the claims.

4 What is claimed is: 1. A tone generator system for electronic musical instruments having variable load circuit means, comprising: regenerative tone generator means having output means which alternately develops a low internal impedance and a high internal impedance; and output isolator static passive unidirectional means connected between said output means and said load circuit means, said output isolator means being operative to connect said generator means to the load circuit means during periods of low internal generator impedance and disconnect it from said load circuit means during periods of higher internal impedance whereby the frequency of the tone generator means is unaffected by variations in said load circuit means. 2. In the tone generator system defined in claim 1, said isolator means comprising a diode poled for nonconduction during high internal impedance of the output means,

3. A tone generator system for electronic musical instruments, comprising:

a regenerative tone oscillator utilizing a transistor; said transistor operating in a regular recurring cycle of (a) heavy conduction, followed by: (h) light conduction; (c) a return to heavy conduction; and a diode output isolator connected to said transistor, and having variable external loading and a direct current power source connected to the side of said diode isolator opposite said tone oscillator, said diode isolator being poled to conduct during heavy conduction of the transistor and to substantially disconnect the external loading during the periods of light conduction of said transistor, whereby the frequency of the tone generator is unaffected by variations in said external loading. 4. A tone generator system for electronic musical instruments comprising:

regenerative tone generator means having a three element current valve having first, second, and

third elements, said third element controlling the impedance between the first and second elements operative to shift the impedance recurrently between high and low values, a variable load circuit fed by the tone generator means, and an isolator network connecting the load circuit to the first and second valve elements comprising series diode means, a source of DC. voltage, and resistance means connecting said source to said diode means adjacent the load circuit, said diode means being poled to block current flow during high impedance between the first and second elements, whereby the frequency of the tone generator means is unatTected by variations in said load circuit. 5. A tone generator system for electronic musical instruments having variable load circuit means, comprising: regenerative tone generator means having output means which develops an output voltage varying cyclicly between two extremes with a relatively low output impedance during one extreme and a relatively high output impedance during the other extreme, an isolator network connecting the output means of the generator means to the load circuit means comprising series diode means, a source of DC. voltage, and resistance means connecting said source to said diode means adjacent the load circuit, the voltage applied to said diode means by said source being intermediate the output voltage extremes and the diode means being poled to block said other extreme of output voltage from said source, whereby the frequency of the tone generator means is unaffected by variations in said load circuit means.

(References on foliowing page) References Cited by the Examiner UNITED STATES PATENTS Warnock 30'7-88.5 Walsh et a1. 331109 Gerr 307-885 J Wagner 331-109 6 OTHER REFERENCES Millman and Taub: Pulse and Digital Circuits, Mc- Graw-Hill Book Co., Inc., 1956, FIG. 47(d), page 111.

ARTHUR GAUSS, Primary Examiner.

J. HEYMAN, J. ZAZWORSKY, Assistant Examiners. 

1. A TONE GENERATOR SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS HAVING VARIABLE LOAD CIRCUIT MEANS, COMPRISING: REGENERATIVE TONE GENERATOR MEANS HAVING OUTPUT MEANS WHICH ALTERNATELY DEVELOPS A LOW INTERNAL IMPEDANCE AND A HIGH INTERNAL IMPEDANCE; AND OUTPUT ISOLATOR STATIC PASSIVE UNIDIRECTIONAL MEANS CONNECTED BETWEEN SAID OUTPUT MEANS AND SAID LOAD CIRCUIT MEANS, SAID OUTPUT ISOLATOR MEANS BEING OPERATIVE TO CONNECT SAID GENERATOR MEANS TO THE LOAD CIRCUIT MEANS DURING PERIODS OF LOW INTERNAL GENERATOR IMPEDANCE AND DISCONNECT IT FROM SAID LOAD CIRCUIT MEANS DURING PERIODS OF HIGHER INTERNAL IMPEDANCE WHEREBY THE FREQUENCY OF THE TONE GENERATOR MEANS IS UNAFFECTED BY VARIATIONS IN SAID LOAD CIRCUIT MEANS. 